Electronic imager using an impedance sensor grid array and method of making

ABSTRACT

An novel impedance sensor is provided having a plurality of substantially parallel drive lines configured to transmit a signal into a surface of a proximally located object, and also a plurality of substantially parallel pickup lines oriented substantially perpendicular to the drive lines and separated from the pickup lines by a dielectric to form intrinsic electrode pairs that are impedance sensitive at each of the drive and pickup crossover locations.

RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No. 12/688,790, filed Jan. 15, 2010, now U.S. Pat. No. 8,421,890, which is hereby incorporated herein by reference in its entirety.

BACKGROUND

The invention is generally related to electronic sensing devices, and, more particularly, to sensors for sensing objects located near or about the sensor.

In the electronic sensing market, there are a wide variety of sensors for sensing objects at a given location. Such sensors are configured to sense electronic characteristics of an object in order to sense presence of an object near or about the sensor, physical characteristics of the object, shapes, textures on surfaces of an object, material composition, biological information, and other features and characteristics of an object being sensed.

Sensors may be configured to passively detect characteristics of an object, by measuring such as temperature, weight, or various emissions such as photonic, magnetic or atomic, of an object in close proximity or contact with the sensor, or other characteristic. An example of this is a non-contact infrared thermometer that detects the black body radiation spectra emitted from an object, from which its temperature can be computed.

Other sensors work by directly exciting an object with a stimulus such as voltage or current, then using the resultant signal to determine the physical or electrical characteristics of an object. An example of this is a fluid detector consisting of two terminals, one that excites the medium with a voltage source, while the second measures the current flow to determine the presence of a conductive fluid such as water.

Since a single point measurement of an object often does not provide enough information about an object, it is often advantageous to collect a 2-dimensional array of measurements. A two dimensional array of impedance may be created by moving a line sensing array over the surface of an object and then doing a line by line reconstruction of a two dimensional image like a fax machine does. An example of this is a swiped capacitive fingerprint sensor that measures differences in capacitance between fingerprint ridges and valleys as a finger is dragged across it. Such sensors reconstruct a two dimensional fingerprint image after the fact using individual line information.

A simpler way to obtain a two dimensional image is to create a two dimensional sensing array. Such sensors however can be prohibitive in cost due to the large number of sensing points needed in the array. An example of this is a two dimensional capacitive fingerprint sensor. A number of these are currently manufactured but use 150 mm² or more of silicon area and are therefore cost prohibitive for many applications.

These different types of electronic sensors have been used in various applications, such as biometric sensors for measuring biological features and characteristics of people such as fingerprints, medical applications such as medical monitoring devices, fluid measuring monitors, and many other sensor applications. Typically, the sensing elements of the various devices are connected to a processor configured to process object information and to enable interpretations for object features and characteristics.

There are many applications for two dimensional image sensors as a particular example, and innovators have struggled with state of the art technology that has come short of desired features and functions. Fingerprint sensors, for example, have been in existence for many years and used in many environments to verify identification, to provide access to restricted areas and information, and many other uses. In this patent application, different types of fingerprint sensors will be highlighted as examples of sensor applications where the present invention is applicable for simplicity of explanations, but other types of applications are also relevant to this background discussion and will also be addressed by the detailed description of the invention. These placement sensors may be configured to sense objects placed near or about the sensor, such as a fingerprint placement sensor that is configured to capture a full image of a fingerprint from a user's finger and compare the captured image with a stored image for authentication. Alternatively, sensors may be configured to sense the dynamic movement of an object about the sensor, such as a fingerprint swipe sensor that captures partial images of a fingerprint, reconstructs the fingerprint image, and compares the captured image to a stored image for authentication.

In such applications, cost, though always a factor in commercial products, has not been so critical—accuracy and reliability have been and still remain paramount factors. Typically, the placement sensor, a two-dimensional grid of sensors that senses a fingerprint image from a user's fingerprint surface all at once, was the obvious choice, and its many designs have become standard in most applications. Once the fingerprint image is sensed and reproduced in a digital form in a device, it is compared against a prerecorded and stored image, and authentication is complete when there is a match between the captured fingerprint image and the stored image. In recent years, fingerprint sensors have been finding their way into portable devices such as laptop computers, hand held devices, cellular telephones, and other devices. Though accuracy and reliability are still important, cost of the system components is very important. The conventional placement sensors were and still are very expensive for one primary reason: they all used silicon sensor surfaces. These surfaces are very expensive, as the silicon material is as expensive as the material to make a computer chip. Computer chips, of course, have become smaller over the years to reduce their cost and improve their performance. The reason the fingerprint silicon could not be made smaller: they need to remain the size of the average fingerprint, and the requirement for full scanning of the users' fingerprints simply cannot be compromised. The full print is required for adequate security in authentication.

Enter the fingerprint swipe sensor into the market. Swipe sensors are fundamentally designed with a line sensor configured to sense fingerprint features as a user swipes their finger in a perpendicular direction with respect to the sensor line. The cost saver: swipe sensors need much less silicon, only enough to configure a line sensor with an array of pixel sensors. The width is still fixed based on the average fingerprint width, but the depth is substantially smaller compared to the placement sensor. Some swipe sensors are capacitive sensors, where capacitance of the fingerprint surface is measured and recorded line by line. Others send a small signal pulse burst into the surface of the fingerprint surface and measure response in a pickup line, again recording fingerprint features line by line. In either case, unlike the placement sensors, the full fingerprint image needs to be reconstructed after the user completes the swipe, and the individual lines are reassembled and rendered to produce a full fingerprint image. This image is compared with a fingerprint image stored in the laptop or other device, and a user will then be authenticated if there is an adequate match.

For the capacitive swipe sensors, the first generation sensors were constructed with direct current (DC) switched capacitor technology (for example U.S. Pat. No. 6,011,859). This approach required using two plates per pixel forming a capacitor between them, allowing the local presence of a finger ridge to change the value of that capacitor relative to air. These DC capacitive configurations took images from the fingerprint surface, and did not penetrate below the finger surface. Thus, they were easy to spoof, or fake a fingerprint with different deceptive techniques, and they also had poor performance when a user had dry fingers. RF (Radio Frequency) sensors were later introduced, because some were able to read past the surface and into inner layers of a user's finger to sense a fingerprint. Different radio frequencies have been utilized by various devices along with different forms of detection including amplitude modulation (AM) and, phase modulation (PM). There are also differing configurations of transmitters and receivers, one type (for example U.S. Pat. No. 5,963,679) uses a single transmitter ring and an array of multiple low quality receivers that are optimized for on chip sensing. In contrast another type (for example U.S. Pat. No. 7,099,496) uses a large array of RF transmitters with only one very high quality receiver in a comb like plate structure optimized for off chip sensing.

One key impediment to the development of low cost placement sensors has been the issue of pixel density, and the resultant requirement for a large number of interconnections between layers of the sensor device. A typical sensor for a fingerprint application will be on the order of 10 mm×10 mm, with a resolution of 500 dpi. Such a sensor array would be approximately 200 rows by 200 columns, meaning there would need to be 200 via connections between layers in the device. While semiconductor vias can be quite small, the cost for implementing a sensor in silicon has proven to be prohibitive, as mentioned above.

In order to produce a placement sensor at a low enough cost for mass market adoption, lower cost processes such as circuit board etching must be employed. The current state of the art in circuit board via pitch is on the order of 200 um, vs. the 50 um pitch of the sensor array itself. Additionally, the added process steps required to form vias between layers of a circuit board significantly increase the tolerances for the minimum pitch of traces on each of the layers. Single-sided circuits may be readily fabricated with high yield with line pitch as low as 35 um, whereas double sided circuits require a minimum line pitch on the order of 60 um or more, which is too coarse to implement a full 500 dpi sensor array. One further consideration is that at similar line densities, double-sided circuits with vias are several times more expensive per unit area than single sided, making high-density double sided circuits too expensive for low cost sensor applications.

For laptop devices, adoption of the swipe sensor was driven by cost. The swipe sensor was substantially less expensive compared to the placement sensors, and most manufacturers of laptops adopted them based solely on price. The cost savings is a result of using less silicon area. More recently a substitute for the silicon sensor arose, using plastic Kapton™ tape with etched sensing plates on it, connected to a separate processor chip (for example U.S. Pat. No. 7,099,496). This allowed the silicon portion of the sensor to be separated from the sensing elements and the silicon to follow Moore's law, shrinking to an optimal size, in length, width and depth in proportion to advances in process technology. Although this advance in the art enabled cheap durable Swipe Sensors, it did not overcome the basic image reconstruction and ergonomics issues resulting from changing from a simple two dimensional placement format. In addition to Swipe Sensors being cheaper, they take up less real estate in a host device, whether it is a laptop or a smaller device, such as a cellular phone or personal data device.

In most swipe class sensors, the fingerprint reconstruction process turned out to be a greater ergonomic challenge to users and more of a burden to quality control engineers than initially expected. Users needed to be trained to swipe their finger in a substantially straight and linear direction perpendicular to the sensor line as well as controlling contact pressure. Software training programs were written to help the user become more proficient, but different environmental factors and the inability of some to repeat the motion reliably gave Swipe Sensors a reputation for being difficult to use. Initial data from the field indicated that a large number of people were not regularly using the Swipe Sensors in the devices that they had purchased and opted back to using passwords. Quality control engineers who tried to achieve the optimum accuracy and performance in the matching process between the captured and reconstructed image found that the number of False Rejects (FRR), and False Acceptances (FAR), were much higher in Swipe Sensors than in placement sensors. Attempts to improve these reconstruction algorithms failed to produce equivalent statistical performance to placement sensors.

Other claims of the Swipe Sensor such as the use of less host real estate did not pan out. Various ramps, wells and finger guides had to be incorporated into the surfaces of the host devices to assist the user with finger placement and swiping. These structures ended up consuming significant space in addition to the actual sensor area. In the end, swipe sensors ended up taking up almost as much space as the placement sensors. This was not a big problem for full size laptops, but is currently a substantial problem for smaller laptops and netbooks, mobile phones, PDAs, and other small devices like key fobs.

Real estate issues have become even more of an issue with mobile device manufacturers who now require that the fingerprint sensor act also as a navigation device, like a mouse or touch-pad does in a laptop. The swipe sensor has proved to be a poor substitute for a mouse or touch pad due to the fact that they are constructed with an asymmetric array of pixels. Swipe sensors do a good job of detecting motion in the normal axis of the finger swipe but have difficulty accurately tracking sideways motion. Off axis angular movements are even more difficult to sense, and require significant processor resources to interpolate that movement with respect to the sensor line, and often have trouble resolving large angles. The byproduct of all this is a motion that is not fluid and difficult to use.

It is clear that low cost two dimensional fingerprint sensor arrays would serve a market need, but present art has not been able to fill that need. Conventional capacitive fingerprint sensors typically use distinct electrode structures to form the sensing pixels array. These electrode structures are typically square or circular and can be configured in a parallel plate configuration (for example U.S. Pat. Nos. 5,325,442 and 5,963,679) or a coplanar configuration (for example U.S. Pat. No. 6,011,859 and U.S. Pat. No. 7,099,496).

These prior art approaches cannot be configured into a low cost two dimensional array of sensing elements. Many capacitive fingerprint sensors (for example U.S. Pat. Nos. 5,963,679 and 6,011,859) have plate structures that must be connected to the drive and sense electronics with an interconnect density that is not practical for implementation other than using the fine line multilayer routing capabilities of silicon chips and therefore require lots of expensive silicon die are as stated before. Other sensors (for example U.S. Pat. No. 7,099,496) use off chip sensing elements on a cheap polymer film, but the sensor cell architecture is inherently one dimensional and cannot be expanded into a two dimensional matrix.

Another application for capacitive sensing arrays has been in the area of touch pads and touch screens. Because touchpad and touch screen devices consist of arrays of drive and sense traces and distinct sense electrodes, they are incapable of resolutions below a few hundred microns, making this technology unsuitable for detailed imaging applications. These devices are capable of detecting finger contact or proximity, but they provide neither the spatial resolution nor the gray-scale resolution within the body of the object being sensed necessary to detect fine features such as ridges or valleys.

Conventional art in the touchpad field utilizes a series of electrodes, either conductively (for example U.S. Pat. No. 5,495,077) or capacitively (for example US publication 2006/0097991). This series of electrodes are typically coupled to the drive and sense traces. In operation these devices produce a pixel that is significantly larger in scale than the interconnect traces themselves. The purpose is to generally sense presence and motion of an object to enable a user to navigate a cursor, to select an object on a screen, or to move a page illustrated on a screen. Thus, these devices operate at a low resolution when sensing adjacent objects.

Thus, there exists a need in the art for an improved device that can provide high quality and accurate placement sensors for use in different applications, such as fingerprint sensing and authentication for example, and that can also operate as a navigation device such as a mouse or touch pad. As will be seen, the invention provides such a device that addresses these and other sensor needs in an elegant manner.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts a diagrammatic view of one embodiment of the invention showing the drive and pickup plate structures with an insulating dielectric layer separating the drive and pickup lines.

FIG. 2 depicts a basic diagrammatic view of one embodiment of the invention showing the basic electrical field operation without an object in close proximity to the drive and pickup plate structures with one drive plate excited by a voltage source.

FIG. 3 depicts a basic diagrammatic view of one embodiment of the invention showing the basic electrical field operation with an object in close proximity to the drive and pickup plate structures with one drive plate excited by a voltage source.

FIG. 4 depicts a basic diagrammatic view of one embodiment of the sensor showing the differences in field intensity with and without an object in close proximity to the drive and pickup plate structures with one drive plate excited by a voltage source.

FIG. 5 depicts a basic diagrammatic view of one embodiment of the invention showing the basic electrical field operation with an object in close proximity of the drive and pickup plate structures with the selected pickup plate amplified and all inactive drive and pickup plates grounded.

FIG. 6a depicts a basic diagrammatic view of one embodiment of the invention showing the basic electrical field operation with a finger or object containing a ridge surface feature in close proximity to the active electrode pair.

FIG. 6b depicts a basic diagrammatic view of one embodiment of the invention showing the basic electrical field operation with a finger or object containing a valley surface feature in close proximity to the active electrode pair.

FIG. 7 depicts a diagrammatic view of an x-y grid of plate rows and columns depicted by lumped circuit components that represent the electric field couplings of the sensor at each drive/pickup crossover.

FIG. 8 depicts an example of an embodiment of the placement invention using a differential amplifier to take the signal from the selected pickup plate and subtract it from a reference signal plate for noise reduction purposes.

FIG. 9a depicts the drive and sense multiplexing circuitry of an embodiment of the invention which incorporates a tank circuit to compensate for input loading effects.

FIG. 9b depicts the drive and sense multiplexing circuitry of an embodiment of the invention which incorporates cascaded buffers to minimize input loading effects.

FIG. 9c depicts the drive and sense multiplexing circuitry of an embodiment of the invention which incorporates dedicated buffers for each sense to minimize loading effects.

FIG. 10 depicts an embodiment of the invention which incorporates an analog receiver to process the sensed signal, and processing circuitry to perform the drive and sense line scanning function.

FIG. 11 depicts an embodiment of the invention which incorporates a direct digital conversion receiver to process the sensed signal, and processing circuitry to perform the drive and sense line scanning function.

FIG. 12 depicts the layout of the drive and sense traces for an embodiment of the invention which incorporates the folded aspect of the invention laid out flat prior to folding.

FIG. 13a depicts the layer stack-up of an embodiment of the invention which incorporates the folding aspect subsequent to folding.

FIG. 13b depicts an embodiment of the invention which incorporates the folding aspect subsequent to folding and assembly into a rigid module.

FIG. 14 depicts a sensor system configured according to the invention for the purpose of sensing features of an object.

FIG. 15 depicts a diagrammatic view of the sensing of a fingerprint features utilizing the invention.

FIG. 16 depicts the process flow steps required to collect a 2-dimensional image with a sensor system configured according to the invention.

FIG. 17a depicts the process flow steps required to authenticate a user with a fingerprint sensor system configured according to the invention.

FIG. 17b depicts the process of template extraction from a fingerprint image typically utilized in user authentication applications.

DETAILED DESCRIPTION

As discussed in the background, there are many applications for a two dimensional impedance sensor, and the invention provides a broad solution to shortcomings in the prior art for many applications. Generally, the invention is directed to a two-dimensional sensor having sensor lines located on a substrate, such as a flexible substrate for example, that can be folded over on itself to form a grid array with separate sensor lines orthogonal to each other, where the crossover locations of different sensor lines create sensing locations for gathering information of the features and/or characteristics of an object.

In one embodiment, the drive lines and pickup lines are not electrically intersecting or connected in a manner in which they would conduct with each other, they form an impedance sensing electrode pair with a separation that allows the drive lines to project an electrical field hand the pickup lines to receive an electrical field, eliminating the need for distinct electrode structures. The two lines crossing with interspersed dielectric intrinsically creates an impedance sensing electrode pair. Thus, the sensor is configured to activate two one-dimensional sensor lines to obtain one pixel of information that indentifies features and/or characteristics of an object. Unlike conventional sensors, a sensor configured according to the invention provides a two dimensional grid that is capable of capturing multiple pixels of information from an object by activating individual pairs of drive and pickup lines and capturing the resultant signal. This signal can be processed with logic or processor circuitry to define features and/or characteristics of an object. For example, the information may be used to produce renderings of an object, such as a fingerprint, and compare the renderings to secured information for authentication.

According to one embodiment of the invention, and in contrast to conventional approaches, a device can utilize the intrinsic impedance sensing electrode pair formed at the crossings between the drive and pickup lines. In operation, the electric fields may be further focused by grounding drive and pickup lines near or about the area being sensed by the particular crossover location at one time. This prevents interference that may occur if other drive and pickup lines were sensing electric fields simultaneously. More than one electrode pair may be sensed simultaneously. However, where resolution is an important factor, it may be preferred to avoid sensing electrode pairs that are too close to each other to avoid interference and maintain accuracy in sensing object features at a particular resolution. For purposes of this description, “intrinsic electrode pair” refers to the use of the impedance sensing electrode pairs that are formed at each of the drive and pickup line crossover locations. Due to the fact that the invention uses each the intrinsic electrode pair at each crossover as a sensing element, no differentiating geometric features exist at individual sensing nodes to distinguish them from the interconnect lines. As a result, the alignment between the drive layers and sense layers is non-critical, which significantly simplifies the manufacturing process.

Grounding the adjacent inactive drive and pickup lines restricts the pixel formed at each intrinsic electrode pair without requiring complex measures such as the dedicated guard rings employed in prior art (for example U.S. Pat. No. 5,963,679). Instead, guard grounds around the pixel are formed dynamically by switching adjacent inactive drive and pickup lines into ground potential. This allows the formation of high density pixel fields with relatively low resolution manufacturing processes, as the minimum pixel pitch for a given process is identical to the minimum feature spacing. This, in turn, enables the use of low cost manufacturing process and materials, which is the key to creating a low cost placement sensor.

In one example, the sensor lines may consist of drive lines on one layer and pickup lines on another layer, where the layers are located over each other in a manner that allows the separate sensor lines, the drive and pickup lines, to cross over each other to form impedance sensing electrode pairs at each crossover location. These crossover locations provide individually focused electrical pickup locations or pixels, or electrode pairs where a number of individual data points of features and/or characteristics of an object can be captured. The high degree of field focus is due to the small size of the intrinsic electrode pairs, as well as the high density of the neighboring ground provided by the inactive plates. The flexible substrate may have a second substrate configured with logic or processor circuitry for sending and receiving signals with the sensor lines to electronically capture information related to the object. Alternatively, there may be two separate substrates carrying the separate sensor lines and layered on each other, and yet connected to a third substrate for connection to logic or processor circuitry.

The utilization of the crossover locations between perpendicular lines on adjacent layers for the pickup cell greatly reduces the alignment requirements between the layers. Since there are no unique features at a sensor pixel location to align, the only real alignment requirement between the layers is maintaining perpendicularity. If the sense cell locations had specific features, such as the parallel plate features typical of prior art fingerprint sensors, the alignment requirements would include X and Y position tolerance of less than one quarter a pixel size, which would translate to less than +/−12 um in each axis for a 500 DPI resolution fingerprint application.

In operation, a drive line is activated, with a current source for example, and a pickup line is connected to a receiving circuit, such as an amplifier/buffer circuit, so that the resulting electric field can be captured. An electric field extends from the drive line to the pickup line through the intermediate dielectric insulating layer. If an object is present, some or all of the electric field may be absorbed by the object, changing the manner in which the electric field is received by the pickup line. This changes the resulting signal that is captured and processed by the pickup line and receiving circuit, and thus is indicative of the presence of an object, and the features and characteristics of the object may be sensed and identified by processing the signal. This processing may be done by some form of logic or processing circuitry.

In other embodiments, the signal driving the drive line may be a complex signal, may be a varying frequency and/or amplitude, or other signal. This would enable a sensor to analyze the features and/or characteristics of an object from different perspectives utilizing a varying or complex signal. The signal may include simultaneous signals of different frequencies and/or amplitudes that would produce resultant signals that vary in different manners after being partially or fully absorbed by the object, indicating different features and characteristics of the object. The signal may include different tones, signals configured as chirp ramps, and other signals. Processing or logic circuitry may then be used to disseminate various information and data points from the resultant signal.

In operation, the varying or complex signal may be applied to the drive line, and the pickup line would receive the resulting electric field to be processed. Logic or processing circuitry may be configured to process the resulting signal, such as separating out different frequencies if simultaneous signals are used, so that features and/or characteristics of the object may be obtained from different perspectives.

Given the grid of pixels that can be activated at individual pairs, each pixel may be captured in a number of ways. In one embodiment, a drive line may be activated, and pickup lines may be turned on and off in a sequence to capture a line of pixels. This sequencing may operate as a scanning sequence. Here a first drive line is activated by connecting it to a signal source, and then one pickup line is connected to amplifier/buffer circuitry at a time, the information from the pixel formed at the crossing of the two lines is captured, and then disconnected. Then, a next pixel is processed in sequence, then another, then another, until the entire array of pickup lines is processed. The drive line is then deactivated, and another drive line is activated, and the pickup lines are again scanned with this active drive line. These may be done one at a time in sequence, several non-adjacent pixels may be processed simultaneously, or other variations are possible for a given application. After the grid of pixels is processed, then a rendering of object information will be possible.

Referring to FIG. 1, a diagrammatic view of one embodiment of a sensor 100 configured according to one embodiment of the invention the invention is illustrated. In this configuration, pickup lines or top plates 102 a[m], 102 b[m+1] are located on a insulating dielectric substrate layer 104 and configured to transmit a signal into a surface of an object located in close proximity to the sensor lines. Drive lines or bottom plates 106 a[n], 106 b[n+1] are juxtaposed and substantially perpendicular to the drive lines or plates and are located on an opposite side of the a insulating dielectric substrate to form a type of a grid. The pickup lines are configured to receive the transmitted electromagnetic fields modified by the impedance characteristics on an object placed within the range of those electric fields.

Referring to FIG. 2, a diagrammatic view of a sensor 200 is shown having pickup lines or top plates 202 a, 202 b and insulating layer 204, and drive lines or bottom plates 206 a, 206 b. The Figure further illustrates how electromagnetic fields 208 a, 208 b extend between the drive lines and pickup plates through the substrate. Without an object within proximity, the electric field lines are uniform within the sensor structure and between the different lines. When an object is present, a portion of the electric field lines are absorbed by the object and do not return to the pickup plates through the insulating layer.

Referring to FIG. 3, an object 310 is illustrated proximate the sensor 300. The sensor 300 has pickup lines or top plates 302 a, 302 b, an insulating dielectric layer 304, and drive lines or bottom plates 306 a, 306 b. In operation, the drive lines and pickup lines of this device example may be individually activated, where a drive line/pickup line pair is activated to produce an active circuit. The result is a circuit that transmits electric field from active drive plate 316 into the combined dielectric of the insulating layer 304 and object 310 via electric field lines, 306 a, 306 b, and received by the active pickup plate. As the illustration shows, some of the field lines are captured by the object when it is placed about the active electrode pair. The variations in an object, such as peaks and valleys and other features of an object surface, can be detected and captured electronically by capturing and recording the resulting electric field variations occurring at different crossover locations of the drive and pickup lines. Similar to common capacitance based placement sensors, the sensor can capture a type of image of the object surface electronically, and generate a representation of the features and characteristics of an object, such as the features and characteristics of a fingerprint in the fingerprint sensor example described below.

In this configuration of FIG. 3, only one active electrode pair is illustrated. However, the invention is not limited to this particular configuration, where one single electrode pair, several electrode pairs, or even all electrode pairs may be active at one time for different operations. In practice, it may be desirable for less than all of the electrode pairs to be active at a given time, so that any interference that may occur between close-by pixels would be minimized. In one embodiment, a drive line may be activated, and the pickup lines may be scanned one or more at a time so that a line of pixels can be captured along the drive line and pickup lines as they are paired along a line at the crossover locations. This is discussed in more detail below in connection with FIG. 5.

In general, in operation, each area over which a particular drive line overlaps a pickup line with a separation of the a insulating dielectric substrate is an area that can capture and establish a sensing location that defines characteristics or features of a nearby object about that area. Since there exist multiple sensing locations over the area of the sensor grid, multiple data points defining features or characteristics of a nearby object can be captured by the sensor configuration. Thus, the sensor can operate as a planar two-dimensional sensor, where objects located on or about the sensor can be detected and their features and characteristics determined.

As described in the embodiments and examples below, the invention is not limited to any particular configuration or orientation described, but is only limited to the appended claims, their equivalents, and also future claims submitted in this and related applications and their equivalents. Also, many configurations, dimensions, geometries, and other features and physical and operational characteristics of any particular embodiment or example may vary in different applications without departing from the spirit and scope of the invention, which, again, are defined by the appended claims, their equivalents, and also future claims submitted in this and related applications and their equivalents.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the invention can be practiced without these specific details. In other instances, well known circuits, components, algorithms, and processes have not been shown in detail or have been illustrated in schematic or block diagram form in order not to obscure the invention in unnecessary detail. Additionally, for the most part, details concerning materials, tooling, process timing, circuit layout, and die design have been omitted inasmuch as such details are not considered necessary to obtain a complete understanding of the invention and are considered to be within the understanding of persons of ordinary skill in the relevant art. Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, components may be referred to by different names. This document does not intend to distinguish between components that differ in name, but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .”

Embodiments of the invention are described herein. Those of ordinary skill in the art will realize that the following detailed description of the invention is illustrative only and is not intended to be in any way limiting. Other embodiments of the invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will be made in detail to implementations of the invention as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts.

In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.

In one embodiment, a sensor device includes drive lines located on or about an insulating dielectric substrate and configured to transmit a signal onto a surface of an object being sensed. Pickup lines are located near or about the drive lines and configured to receive the transmitted signal from the surface of an object. In order to keep a separation between the drive lines and pickup lines, the substrate may act as an insulating dielectric or spacing layer. The substrate may be for example a flexible polymer based substrate. One example is Kapton™ tape, which is widely used in flexible circuits such as those used in printer cartridges and other devices. The package may include such a flexible substrate, where the drive lines may be located on one side of the substrate, and the pickup lines may be located on an opposite side of the substrate.

The drive lines may be orthogonal in direction with respect to the pickup lines, and may be substantially perpendicular to the pickup lines. According to one embodiment of the invention, a device may be configured with drive lines and pickup lines located on or about opposite sides of an insulating dielectric substrate, where the combination of these three components provides capacitive properties. The drive lines may be activated to drive an electric field onto, into or about an object. The pickup lines can receive electronic fields that originated from the drive lines, and these electronic fields can be interpreted by processing or logic circuitry to interpret features or characteristics of the object being sensed.

Thus, in one embodiment the layer separating the drive lines from the pickup lines can provide a capacitive property to the assembly. If some or all of the drive lines are substantially perpendicular to the pickup lines, either entirely or in portions, then a grid may be formed. In such a configuration, from a three dimensional view, the drive lines are located and oriented substantially in parallel with respect to each other about a first plane. One surface of the substrate is located about the drive lines in a second plane that is substantially parallel relative to the drive lines. The pickup lines are located and oriented substantially in parallel with respect to each other about a third plane that is substantially parallel to the first and second planes and also located about another substrate surface that is opposite that of the drive lines, such that the substrate is located substantially between the drive lines and the pickup lines.

In this description, including descriptions of embodiments and examples, there will be references to the terms parallel, perpendicular, orthogonal and related terms and description. It is not intended, nor would it be understood by those skilled in the art that these descriptions are at all limiting. To the contrary, the invention extends to orientations and configurations of the drive lines, the pickup lines, the substrate or related structure, and also various combinations and permutations of components, their placement, distance from each other, and order in different assemblies of a sensor. Though the invention is directed to a sensor configured with plurality of drive and pickup lines that generally cross over each other at a pixel location and are configured to detect presence and other features and characteristics of a nearby object, the invention is not limited to any particular configuration or orientation, but is only limited to the appended claims, their equivalents, and also future claims submitted in this and related applications and their equivalents.

Also, reference will be made to different orientations of the geometric planes on which various components will lie, such as the drive and pickup lines and the substrate that may be placed in between the sets of drive and pickup lines. If flexible substrates are used for example, the use of such a structure will allow for planes to change as a flexible structure is flexed or otherwise formed or configured. In such embodiment will be understood that certain aspects of the invention are directed to the drive lines and pickup lines being configured on opposite sides of a substrate and in a manner that enables the sensing of particular features and/or characteristics of a nearby object at each crossover location of a drive line and a pickup line. Thus, the orientation of the planes (which may be deformable, and thus may be sheets separated by a substantially uniform distance) of groups of components (such as drive lines or pickup lines for example) or substrates may vary in different applications without departing from the spirit and scope of the invention.

Also, reference will be made to pickup lines, pickup plates, drive lines, drive plate, and the like, but it will be understood that the various references to lines or plates may be used interchangeably and do not limit the invention to any particular form, geometry, cross-sectional shape, varying diameter or cross-sectional dimensions, length, width, height, depth, or other physical dimension of such components. Also, more sophisticated components may be implemented to improve the performance of a device configured according to the invention, such as for example small 65, 45, 32 or 22 nanometer conduction lines or carbon nano-tubes that may make an assembly more easily adapted to applications where small size and shape as well as low power are desired characteristics and features. Those skilled in the art will understand that such dimensions can vary in different applications, and even possibly improve the performance or lower power consumption in some applications, without departing from the spirit and scope of the invention.

Reference will also be made to various components that are juxtaposed, layered, or otherwise placed on each other. In one example of an embodiment configured according to the invention, a plurality of drive lines are juxtaposed on one surface of a generally planar substrate, and a plurality of pickup lines are juxtaposed on an opposite surface of the planar substrate. The drive lines are substantially orthogonal to the pickup lines, and may be described as substantially perpendicular to the pickup lines. The distance between the drive lines and pickup lines may be filled with a substrate or insulating material that will provide for a capacitive configuration. Here the drive lines on one side of the substrate forms one capacitive plate, and the pickup lines on an opposite side for the corresponding capacitive plate. In operation, when the drive plate is activated, an electrical field is generated between the drive lines and pickup lines and through the substrate to form a plurality of capacitive elements. These capacitive elements are located at an area at each cross-section of a drive line and a pickup line with a portion of the substrate located between the areas. This is a location where the respective drive lines and pickup lines overlap each other. In any particular application, these areas in which the three components interact during operation define a data location at which a sensor reading can be made.

Reference will also be made to sensor lines, such as sensor drive lines and sensor pickup lines, and their orientation amongst themselves and each other. For example, there will be described substantially parallel drive lines. These drive lines are intended to be described as parallel conductive lines made up of a conductive material formed, etched, deposited or printed onto the surface such as copper, tin, silver and gold. Those skilled in the art will understand that, with the inherent imperfections in most any manufacturing process, such conductive lines are seldom “perfect” in nature, and are thus not exactly parallel in practice. Therefore, they are described as “substantially parallel”. Different applications may configure some of the drive lines even non-parallel, such that the lines may occur parallel for a portion of the line, and the line may necessarily deviate from parallel in order to connect with other components for the device to operate, or in order to be routed on or about the substrate on which it is formed or traced. Similarly, the separate array of lines may be described as orthogonal or perpendicular, where the drive lines are substantially orthogonal or perpendicular to the pickup lines. Those skilled in the art will understand that the various lines may not be perfectly perpendicular to each other, and they may be configured to be off-perpendicular or otherwise crossed-over in different angles in particular applications. They also may be partially perpendicular, where portions of drive lines may be substantially perpendicular to corresponding portions of pickup lines, and other portions of the different lines may deviate from perpendicular in order to be routed on or about the substrate or to be connected to other components for the device to operate.

These and other benefits provided by the invention will be described in connection with particular examples of embodiments of the invention and also descriptions of intended operational features and characteristics of devices and systems configured according to the invention.

In operation, generally, the drive lines can transmit an electromagnetic field toward an object that is proximal to the device. The pickup lines may receive a signal originating from the drive lines and then transmitted through the object and through the substrate and onto the pickup lines. The pickup lines may alternatively receive a signal originating from the drive lines that were then transmitted through the substrate and onto the pickup lines without passing through the object. This electric field can vary at different locations on the grid, giving a resultant signal that can be interpreted by some type of logic or processor circuitry to define features and/or characteristics of an object that is proximate the assembly.

The drive lines and pickup lines may be controlled by one or more processors to enable the transmission of the signal to an object via the drive lines, to receive a resultant signal from an object via the pickup lines, and to process the resultant signal to define an object image. One or more processors may be connected in one monolithic component, where the drive lines and pickup lines are incorporated in a package that includes the processor. In another embodiment, the drive lines, pickup lines and substrate may be assembled in a package by itself, where the package can be connected to a system processor that controls general system functions. This way, the package can be made part of the system by connecting with a system's input/output connections in order to communicate with the system. This would be similar in nature for example to a microphone connected to a laptop, where the audio signals are received by the system processor for use by the laptop in receiving sounds from a user. According to this embodiment of the invention, the sensor can be connected as a stand-alone component that communicates with the system processor to perform sensor operations in concert with the system processor.

In another embodiment of the invention, a sensor may be configured to drive signals at different frequencies since the impedance of most objects, especially human tissue and organs, will greatly vary with frequency. In order to measure complex impedance at one or more frequencies of a sensed object, the receiver must be able also to measure phase as well as amplitude. In one embodiment, the resulting signal generated from a given impedance sensing electrode pair may result from varying frequencies, known in the art as frequency hoping, where the receiver is designed to track a random, pseudo-random or non-random sequence of frequencies. A variation of this embodiment could be a linear or non-linear frequency sweep known as a chip. In such an embodiment one could measure the impedance of a continuous range frequencies very efficiently.

In yet another embodiment of the invention, a grid sensor as described above may be configured to also operate as a pointing device. Such a device could perform such functions as well known touch pads, track balls or mice used in desktops and laptop computers.

In one example of this embodiment, a two dimensional impedance sensor that can measure the ridges and valleys of a finger tip may be configured to track the motion of the fingerprint patterns. Prior art swiped fingerprint sensors can perform this function, but due to the physical asymmetry of the array and the need to speed correct, or “reconstruct” the image in real time make these implementations awkward at best. The sensor could also double as both a fingerprint sensor and a high quality pointing device.

One device configured according to the invention includes a first array of sensor lines on a flexible substrate, and a second array of sensor lines on a flexible substrate, and also a processor configured to process fingerprint data from the first and second arrays of sensor lines. When folded upon itself in the case of a single flexible substrate or when juxtaposed in the case of separate substrates, the separate sensor lines cross each other without electrically shorting to form a grid with cross-over locations that act as pixels from which fingerprint features can be sensed. In one embodiment, an array of substantially parallel sensor drive lines is located on a surface of the flexible substrate. These drive lines are configured to sequentially transmit signal into a surface of a user's finger activating a line at a time. A second array of sensor lines is similar to the first, consisting of substantially parallel sensor pickup lines that are substantially perpendicular to the drive lines. These pickup lines are configured to pick up the signal transmitted from the first.

In the configuration where the first and second set of sensor lines, the drive and the pickup lines for example, are located on different sections of an extended surface of the flexible substrate, the flexible substrate is further configured to be folded onto itself to form a dual layer configuration. Here, the first array of sensor drive lines becomes substantially perpendicular to the second array of pickup sensor lines when the flexible substrate is folded onto itself. This folding process creates crossover locations between these separate arrays of sensor lines—though they must not make direct electrical contact so that they operate independently. These crossover locations represent impedance sensing electrode pairs configured to sense pixels of an object and its sub-features juxtaposed relative to a surface of the flexible substrate. The scanning of these pixels is accomplished by activating individual rows and columns sequentially. Once a drive column is activated with drive signal the perpendicular pickup rows are scanned one at a time over the entire length of the selected driver. Only one row is electrically active (high impedance) at a time, the non active rows are either shorted to ground or multiplexed to a state where they do not cross couple signal. When a finger ridge is placed above an array crossover location that is active, it interrupts a portion of the electric field that otherwise would be radiated through the surface film from the active drive column to the selected row pickup. The placement of an object's subfeature, such as a ridge or valley in the case of a fingerprint sensor, over an impedance sensing electrode pair results in a net signal decrease since some of the electric field is conducted to ground through the human body. In a case of a fingerprint sensor the placement of a fingerprint ridge/valley over an impedance sensing electrode pair, the valley affects the radiation of electric field from the selected drive line to the selected pickup line much less than a ridge would. By comparing the relative intensity of signals between the pixels ridges and valleys, a two dimensional image of a finger surface can be created.

Referring again to FIG. 1, this general example of the grid sensor will be now used to illustrate how such a sensor configured according to the invention can be implemented as a fingerprint sensor, where the object would simply be the surface of the fingerprint on the user's finger. This example will be carried through the following Figures for illustration of the benefits and novel features of the impedance sensor configured according to the invention. However, it will be appreciated by those skilled in the art, however, that any object may be sensed by a device configured according to the invention. Again, the example and description are intended only for illustration purposes.

In operation, the sensor can be configured to detect the presence of a finger surface located proximate to the sensor surface, where the drive lines can drive an active electromagnetic field onto the finger surface, and the pickup lines can receive a resulting electromagnetic field signal from the pickup lines. In operation, the drive lines can generate an electric field that is passed onto the surface of the finger, and the different features of the fingerprint, such as ridges and valleys of the fingerprint surface and possibly human skin characteristics, would cause the resulting signal to change, providing a basis to interpret the signals to produce information related to the fingerprint features.

In one embodiment of a fingerprint sensor, referring again to FIG. 1 in the context of a fingerprint sensor, a flexible substrate is used as the insulating dielectric layer 104, to allow for beneficial properties of durability, low cost, and flexibility. The drive lines or plates 106 a, 106 b, are located on the flexible substrate and configured to transmit a signal into a surface of a user's fingerprint features and structures, such as ridges and valleys, placed on or about the sensor lines. The pickup lines 102 a, 102 b are configured to receive the transmitted signal from the user's finger surface. A processor (not shown) can be configured to collect and store a fingerprint image based on the received signal from the pickup lines.

FIG. 4 illustrates the field interactions of a basic sensor cell.

Referring to FIG. 4, an example a sensor 400 configured as an object sensor, where the top plates or pickup lines 402 a, 402 b, . . . , 402 n are located on one side of insulating dielectric layer or substrate 404. Bottom plates or pickup lines 406 a, 406 b, . . . , 406 n are located on an opposite side of the substrate 404. Electric fields 408 a, 408 b extend from bottom plates or drive lines 406 a, 406 b through the insulating layer or substrate 404 and onto active top plate 402 a. According to the invention, these drive lines may be activated one at a time to reduce any interference effects, but the electric field results illustrated here are intended to illustrate a contrast between electric fields that are partially or fully absorbed by the object with electric fields that are not absorbed the object at all. This information may be collected from drive and pickup plate electrode pairs at each crossover location to sense features and characteristics of the object that is proximate the sensor lines. Partially covered top plate or pickup line 402 b is connected to voltmeter 417, and uncovered top plate 402 a is connected to voltmeter 418. Active drive line or bottom plate 406 b is connected is connected to AC signal source 416, causing an electric field to radiate from active plate 406 b. According to a particular application, the number of drive lines and pickup lines can vary depending on the application, and it may depend on the cost and resolution desired. As can be seen, the electric field lines 408 a is partially captured by the drive lines 402 a and 402 b, and part is captured by the object, in this case finger 410. Also, in order to illustrate that the drive lines and pickup lines will exhibit different reading when an object or object feature is present or not present or proximate to a given crossover location, volt meter 417 illustrates the response to the top plate or drive line 402 b, and voltmeter 418 illustrates the response of top plate or drive line 402 a. The difference in the deflections of voltmeter 417 in comparison 418 show the delta in electric field intensity between the two electrode pair locations, one with a finger present the other without.

Referring to FIG. 5, another example of a sensor configured according to the invention is illustrated the Drive and pickup configuration when detecting the presence of an object. The sensor 500 is illustrated, where the top plates or pickup lines 502 a, 502 b, . . . , 502 n are located on one side of insulating layer or substrate 504, and bottom plates or drive lines 506 a, 506 b, . . . , 506 n are located on an opposite side of the substrate 504. Again, the pickup lines are shown on the layer closest to the object being sensed for maximum sensitivity, and the drive lines shown on the opposite side of the substrate. Electric fields 508 a, 508 b extend from bottom plates or drive lines 506 a, 506 b through the insulating layer or substrate 504 and onto active top plate 502 b. Other configurations are possible, perhaps having drive plates on the top, and pickup plates on the bottom. The invention, however, is not limited to any particular configuration that is insubstantially different than the examples and embodiments disclosed and claimed herein.

FIG. 5, further shows a snapshot of one selected individual electrode pair located at the crossover of pickup line 502 b and drive line 506 b, where the remaining pickup and drive lines are not active, shown grounded in FIG. 5. Drive line 506 b is connected to AC voltage source 516, and pickup line 502 b is connected to amplifier/buffer 514. Once activated as shown here, electric field lines 508 a, 508 b are generated, and they radiate from drive line 506 b and are sensed by pickup line 502 b, sending the resultant signal into amplifier/buffer 514, and are later processed by analog and digital circuit functions. Grounding the inactive adjacent drive and pickup lines focuses the electric fields 508 a and 508 b at the crossover location between the active the drive and pickup plates, limiting crosstalk from adjacent areas on the object being sensed. As the sensing operation proceeds in this embodiment, different drive line/pickup line crossover pairings may be activated to capture different pixels of information from the object. In the case of an object sensor, it can capture information on the shape of the object, and, if the electrical characteristics are non-uniform across its surface, it's composition. Again, the invention is not limited to this particular configuration, where one single electrode pair, several electrode pairs, or even all electrode pairs may be active at one time for different operations. In practice, it may be preferable for less than all of the impedance sensing electrode pairs to be active at a given time, so that any interference that may occur between close-by pixels would be minimized. In one embodiment, a drive line may be activated, and the pickup lines may be scanned one or more at a time so that a line of pixels can be captured along the drive line and pickup lines as they are paired along a line at the crossover locations. Thus, and still referring to FIG. 5, the AC voltage source 516 may remain connected to drive line 506 b, and the connection of the amplifier/buffer 516 may cycle or scan over to sequential pickup lines, so that another pixel of information can be captured from another pickup line crossover paired with drive line 506 b. Once substantially all the pickup lines 506 a-n have been scanned drive line 506 b can be deactivated, than another drive line in sequence can be activated with the AC voltage source, and a new scanning can commence through the pickup lines. Once substantially all drive line/pickup line pairings have been scanned to capture the full two-dimensional array of pixels, then a two dimensional image or rendering of the object features and characteristics can be made, such as a rendering of the shape of the object, and potentially a composition map.

As another example of a sensor that can benefit from the invention, a reduced cost fingerprint swipe sensor could be configured using the same innovation provided by the invention. In this embodiment, a reduced number of pickup lines could be configured with a full number of orthogonal drive lines. Such a configuration would create a multi-line swipe sensor that would take the form of pseudo two-dimensional sensor, and when a finger was swiped over it would create a mosaic of partial images or slices. The benefit of this would be to reduce the complexity of image reconstruction task, which is problematic for current non-contact silicon sensors that rely on one full image line and a second partial one to do speed detection.

The tradeoff would be that this pseudo two dimensional array would have to be scanned at a much faster rate in order to keep up with the varying swipe speeds of fingers that have to be swiped across it.

FIGS. 6a and 6b illustrate the operation of the sensor when detecting surface features of an object such as fingerprint ridges and valleys. The sensor is configured identically to the previous example in FIG. 5, but in this case is interacting with a textured surface such as a fingerprint.

Referring to FIGS. 6a and b , another example of a sensor configured according to the invention is illustrated. The sensor 600 is illustrated, where the top plates or pickup lines 602 a-n are located on one side of insulating layer or substrate 604, and bottom plates or drive lines 606 a-n are located on an opposite side of the substrate 604. For maximum sensitivity pickup lines are shown on the layer closest to the object being sensed, and the drive lines shown on the opposite side of the substrate. FIG. 6a shows electric field lines 620 as they interact with a proximally located object's valley and FIG. 6b shows electric field lines 621 as the interact with a proximally located object's peaks, extending from bottom plate drive line 606 b through the insulating layer or substrate 604 and onto active drive line 606 b. In the case of sensing a fingerprint, the corresponding ridges and valleys over the fingerprint surface can be captured by the grid of drive line/pickup line crossover points, and the resulting data can be used to render an image of the fingerprint. A stored fingerprint can then be compared to the captured fingerprint, and they can be compared for authentication. This is accomplished using any one of many fingerprint matching algorithms which are available from vendors as stand alone products. Such vendors include Digital Persona, BioKey, and Cogent Systems, to name just a few.

Also illustrated in FIGS. 6a and b , is the individual sensor line pairing of pickup line 602 b and drive line 606 b. Their crossover forms the active electrode pair, and the remaining pickup and drive lines are not active, and will nominally be grounded by electronic switches. Drive line 606 b is connected to AC voltage source 616, and pickup line 602 b is connected to amplifier/buffer 605. Once activated as shown here, electric field lines 620 and 621 are created as shown in FIGS. 6a and 6b respectively, and they emanate between the drive line 606 b and pickup line 602 b, sending a resultant signal that is radiated onto pickup line 602 b and connected to amplifier/buffer 605, and later processed by analog and digital processing circuitry. As the sensing operation proceeds in this embodiment, different drive line/pickup line crossover pairs may be activated to capture different pixels of information from the object. In the case of a fingerprint, it can capture information on different features and characteristics of the fingerprint and even the body of the finger itself. Again, the invention is not limited to this particular configuration, where one electrode pair, several electrode pairs, or even all electrode pairs may be active at one time for different operations. In practice, it may be preferable for less than all of the electrode pairs to be active at a given time, so that any interference that may occur between close-by pixels would be minimized. In one embodiment, a drive line may be activated, and the pickup lines may be scanned one or more at a time so that a line of pixels can be captured along the drive line and pickup lines as they are paired along a line at the crossover points. Thus, and still referring to FIG. 6a , the voltage source 616 may remain connected to drive line 606 b, and the connection to buffer/amplifier 605 may cycle or scan over to another pickup line, so that another pixel of information can be captured from another electrode pair using driveline 606 b.

In the snapshot shown in FIGS. 6a and 6b drive plate 606 b remains excited by AC signal source 616 until an entire column of pixels is scanned, while unused drive plates (606 a,c-n etc.), are switched to ground for isolation purposes. Likewise, in one embodiment only one pickup plate is active at a time and some or substantially all other pickup plates are switched to ground to minimize crosstalk.

The scanning process continues beyond the snapshot shown in FIGS. 6a and 6b , with the next column in sequence being activated, 606 c, (although the sequence could be arbitrary), Once the entire sequence of Pickup Plates 602 a-n is scanned, the next driver line 606 d would activated, until all, or substantially all of the drive lines 606 a-n have been sequenced. Once all the drive columns have been activated and the pickup plates scanned for each column, one will have collected a complete two dimensional array of pixels equal to the number of driver rows times the number of pickup columns. For a 500 DPI sensor that would create a 10×10 mm array or 100 mm², consisting of 40,000 individual pixels. Depending on the application, all of the drive lines may be sequenced, or possibly some or most of them may be sequenced.

Referring again to FIGS. 6a and 6b , the two conductive layers Drive layer 606 and Pickup layer 602, are separated by an electrically insulating layer 604. This insulating layer 604 has high DC resistance and has a dielectric constant greater than one to allow the transmission of high frequency electric fields through it. In one embodiment this layer 602 is created by folding a single sided flexible printed circuit board back onto itself. In another embodiment it is created by placing a dielectric layer between two electrically active layers to form a double sided circuit board.

FIG. 7 shows an example of an x-y grid of plate rows and columns depicted by lumped circuit components that represent the electric field couplings of the sensor at each drive/pickup crossover.

The bottom plates 701 a,b,c etc. are driven one at a time by AC signal source 716 via switch matrix 740 a-n. FIG. 7 shows a scan snapshot where one drive switch 740 b in the on condition connecting the corresponding plate to the signal source. This activates one entire row 740 b with AC signal over the entire length of the plate which is equal to the sensor width in one dimension. Correspondingly each column plate 703 a,b,c etc. will pickup up AC signal through insulating layer 704 and coupling capacitors 761 a,b,c . . . n. Only one pickup plate at a time is active being switched into the buffer amplifier 716. Top Plate 702 b is shown as the active plate in FIG. 7, while all or substantially all other pickups are shorted to ground via switch matrix 730 a-n, thus the information from one x-y pixel is captured.

A single row remains active only as long as it takes the entire number of pickup plates/columns to be scanned. Scan time per pixel will depend on the frequency of operation and the settling time of the detection electronics, but there is no need to scan unduly fast as is typical with prior art swipe sensors. On the other hand prior art swipe sensors must scan at a very high pixel rate in order not to lose information due to undersampling relative to the finger speed which can be greater than 20 cm/sec. This reduction in capture speed relative to a swipe sensor relaxes the requirements of the analog electronics and greatly reduces the data rate that a host processor must capture in real time. This not only reduces system cost but allows operation by a host device with much less CPU power and memory. This is critical especially for mobile devices.

Once an entire row 706 b has been scanned by all or substantially all of its corresponding pickup plates 702 a-n, then the next row in the sequence is activated through switch matrix 740. This process continues until all or substantially all of the rows and columns are scanned.

The amount of signal that is coupled into the buffer amplifier 716 is a function of how much capacitance is formed by the insulating layer and the finger ridge or valley in close proximity. The detailed operation of how these electric fields radiate is shown in FIGS. 6a and b . The total coupling capacitance is a series combination of the insulating layer capacitance 704 which is fixed for a given thickness, and the variable topological capacitance of the object being sensed. The variable portion of this is shown in FIG. 7 as a series of variable capacitors numbered 760 a-n, 761 a-n, 762 a-n etc., forming a two dimensional array.

FIG. 8 shows an example of an embodiment of the placement sensor using a differential amplifier 880 to take the signal from the selected pickup plate (802 a-n), and subtract it from the reference signal of plate 805. The electrical subtraction of these signals performs several functions: first wide band common mode is subtracted out; second, subtracting against reference plate 805 provides a relative reference signal equivalent to an ideal ridge valley; third, common mode carrier signal that couples into both plates other than through a finger is also subtracted out. First order carrier cancellation of etch variation in the pickup plates also occurs when we subtract out carrier that is coupled in by other means than through fingers placed on the sensor. This is critical for high volume manufacturing at a low cost.

Reference plate 805 is intentionally located outside of the finger contact area of the sensor, separated from pickup plates 802 a-n by Gap 885, Gap 885 is much larger that the nominal gap between the pickup plates which is typically 50 um. In a real world embodiment plate 805 would be positioned under the plastic of a bezel to prevent finger contact, placing it at least 500 um apart from the other pickup plates.

Each one of the pickup plates 802 a-n is scanned sequentially being switched through pickup switches 830 a-n connecting them to Differential Amplifier 880. During the scanning process of an entire pickup row, the positive leg of the differential amplifier remains connected to reference plate 805 to provide the same signal reference for all of the pickup plates.

FIG. 9a shows a circuit diagram of an example of a front end for the placement sensor in a topology that uses a bank of Single Pole Double Throw Switches or SPDTs to scan the pickup plate rows and a bank of Single Pole Single Throw switches to multiplex the pickup plate columns.

In FIG. 9a we see a snapshot of the analog switches as the scanning process begins. Only the first SPDT switch 1044 a is shown in the “on” position, which allows pickup plate 902 a to conduct its plate signal into Differential Amplifier 980. The remaining pickup plates are shorted to ground via switches 944 a-944 n, preventing any pickup signal received by them from entering into differential amplifier 980.

Each SPDT has a Parasitic Capacitance 945, due to the fact that real world switches to not give perfect isolation. In fact the amount of isolation decreases with frequency, typically modeled by a parallel capacitor across the switch poles. By using a SPDT switch we can shunt this capacitance to ground when an individual plate is not active. Since there is a large array of switches equal to the number of pickup plates, typically 200 for a 500 dpi sensor, the effective shunt capacitance to ground is multiplied by that number. So if a given switch has 0.5 picofarads of parasitic capacitance and there where 200 pickups, that would add up to 100 picofarads of total shunt capacitance.

In order to prevent this large capacitance from diverting most of the received signal from the active pickup to ground, it is desirable in this example to use a compensating circuit. This is accomplished by using resonating inductor 939, forming a classic bandpass filter circuit in conjunction with parasitic capacitors 945 (one per switch) and tuning capacitors 934 and 937. A two step null & peak tuning calibration procedure is used where tuning capacitor 934 and 937 are individually tuned with inductor 939 using the same drive signal on both the plus and minus inputs to differential amplifier 980. The two bandpass filters formed with inductor 1039 and resonating capacitors 934, and 937 respectively, will be tuned to the same center frequency when there is zero signal out of differential amplifier 980. Next capacitors 934 and 937 and inductor 939 are tuned together using a differential input signal with opposite 180 degrees phases on the plus and minus inputs to the differential amplifier 980. They are incremented in lock step until the exact drive carrier frequency is reached, this occurs when the output of differential amplifier 980 is at its peak, making the center frequency equal to the exact frequency of the carrier drive signal 916.

In a systems implementation, a calibration routine would be performed before each fingerprint scan to minimize drift of this filter with time and temperature. The resonating inductor 939 needs to have a Q or Quality Factor of at least 10 to give the filter the proper bandwidth characteristics necessary to optimize the signal to noise ratio.

FIG. 9b shows an alternate example of a device employing multiple banks of plates grouped together, each with their own differential amplifiers.

Dividing up the large number of parallel pickup plates into groups each containing a smaller number of plates is an alternate architecture that would not require the use of a tuned bandpass filter in the front end because the parasitic switch capacitances would be greatly reduced. This would have two possible advantages, first lower cost, and second the ability to have a frequency agile front end. In this Figure we have a snapshot of the front end where the first switch 944 a of bank 907 a is active. All other switch banks 907 a-907 n are shown inactive, shorting their respective plates to ground. Therefore, only voltage or current differential amplifier 980 a has any plate signal conducted into it, voltage or current differential amplifiers 980 b-980 n have both their positive and negative inputs shorted to ground through their respective switches 945 a-n and 945 r, preventing any signal from those banks making a contribution to the overall output.

Each of the differential amplifiers 980 a-980 n are summed through resistors 987 a-987 n into summing amplifier 985. Only the differential amplifier 980 a in this snapshot has plate signal routed into it, so it independently produces signal to the input of summing amplifier 985. This process is repeated sequentially until all or substantially all of the switch banks 907 a-n, and switch plates 944 a-n, 945 a-n, etc, of the entire array are fully scanned.

By splitting the pickup array up, the capacitive input load on each plate is reduced from that of the full array of switches to the number of switches within a given plate group. If we were to divide for example 196 potential pickup plates into 14 banks of 14 plates, resulting in a capacitance load equal to the parasitic capacitance of 14 switches (944), plus the capacitive load of the differential amplifier. If analog switches 944 are constructed with very low parasitic capacitance then the overall input load would be small enough not to need a bandpass circuit in the front end in order to resonate out the load capacitance. As integrated circuit fabrication techniques improve we would be able design smaller switches with less parasitic capacitance, making this approach become more attractive.

FIG. 9c illustrates another example of a front end circuit using individual plate buffers that are multiplexed into a second stage differential amplifier.

Buffers 982 a through 982 n as illustrated are special buffers that are designed to have very low input capacitance. In one embodiment, these buffers could be configured as single stage cascoded amplifiers in order to minimize drain-to-gate Miller capacitance and die area. To better maximize plate to plate isolation, two sets of switches could be used for each input. Analog switches 930 a-930 n are included in this example to multiplex each selected buffer into differential amplifier 980. Switches 932 are included to shut down the power simultaneously to all the other input buffers that are not selected. This effectively puts them at ground potential. An alternate embodiment would be to put input analog switches in front of each amplifier to allow a short of the unused plates directly to ground. One effect of this approach may be an increase in input load capacitance for each plate.

FIG. 9c shows a snapshot of the scanning process where top plate 902 a is being sensed though buffer 982 a which has power supplied to it through switch 932 a. Analog switch 930 a is closed, routing it to differential amplifier 980. All other buffer outputs are disconnected from the differential amplifier 980 via analog switches 930 b-n and power switches 982 b-n

The positive input to differential amplifier 980 is always connected to the reference plate 902 r, providing an “air” signal reference to the amp. The differential amplifier 980 serves to subtract out noise and common mode carrier signal in addition to providing a “air” reference carrier value.

FIG. 10 shows a particular embodiment of a placement sensor implemented with traditional analog receiver technology. The analog front end begins with Differential Amplifier 1080 where selected Pickup Plate 1002 a-n is subtracted from Reference Plate 1005, which is located outside the finger contact area providing a reference signal equivalent to an ideal finger valley. A programmable gain stage or PGA 1090 follows the Differential Amplifier 1090, but could be integrated into the same block providing both gain an subtraction in a single stage. PGA 1090 is designed to have a gain range wide enough to compensate for production variations in plate etching and solder mask thickness between the layers.

Control processor 1030 orchestrates the scanning of the two dimensional sensor plate array. Drive plates/columns 1002 a-1002 n are scanned sequentially by the Drive Plate Scanning Logic 1040 in the Control Processor 1030. When a selected drive plate is activated it is connected to carrier signal source 1016. All inactive drive plates are connected to ground. Before activating the next drive plate in the sequence the active drive plate remains on long enough for the entire row of Pickup Plates 1002 a-n to be scanned by Pickup Plate Logic 1045.

Analog mixer 1074 multiplies the gained up plate signal against the reference carrier 1013. The result is a classic spectrum of base band plus harmonic products at multiples of the carrier frequency. An analog low pass filter 1025 is employed to filter out the unwanted harmonics and must have a sharp enough roll of to attenuate the information associated with of the second harmonic without loosing base band information.

Following the low pass filter is an A/D Converter 1074 that must sample at a least twice the pixel rate to satisfy the Nyquist criteria. Memory buffer 1032 stores the A/D samples locally with sufficient size to keep up with the worst case latency of the host controller. The A/D Sample Control Line 1078 provides a sample clock for the converter to acquire the sequential pixel information that is created by the sequencing of the plate rows and columns.

FIG. 11 shows an example of one embodiment of a placement sensor implemented with direct digital conversion receiver technology. In this example, the analog front end begins with Differential Amplifier 1180 where selected Pickup Plate 1102 a-n is subtracted from Reference Plate 1105, which is located outside the finger contact area providing a reference signal equivalent to an ideal finger valley. The electrical subtraction of these signals performs several functions: first wide band common mode is subtracted out; second, subtracting against reference plate 1105 provides a relative reference signal equivalent to an ideal ridge valley; third, common mode carrier signal that couples into both plates other than through a finger is also subtracted out. Elimination of common mode is particularly important in high RF noise environments. First order carrier cancellation of etch variation in the pickup plates also occurs when we subtract out carrier that is coupled in by other means than through fingers placed on the sensor. This is critical for high volume manufacturing at a low cost.

A programmable gain stage or PGA 1190 follows the Differential Amplifier, which could easily be combined into a single differential amplifier including programmable gain as is commonly done in modern integrated circuit design PGA 1190 is designed to have a gain range wide enough to compensate for production variations in plate etching and solder mask thickness between the layers.

Control processor 1130 orchestrates the scanning of the two dimensional sensor plate array. Drive plates/columns 1102 a-1102 n are scanned sequentially by the Drive Plate Scanning Logic 1140 in the Control Processor 1130. When a selected drive plate is activated it is connected to carrier signal source 1116. All inactive drive plates are connected to ground. Before activating the next drive plate in the sequence the active drive plate remains on long enough for the entire row of Pickup Plates 1102 a-n to scanned by Pickup Plate Logic 1145 and captured by the A/D converter 1125.

The A/D Converter 1125 is sampled at a rate of at least twice the carrier frequency to satisfy the Nyquist criteria. The A/D Sample Control Line 1107 provides a sample clock for the converter to acquire the sequential pixel information that is created by the sequencing of the plate rows and columns.

Following the A/D converter is a Digital Mixer 1118 that digitally multiplies the A/D output which is at the carrier frequency against the reference carrier generated by the Digitally Controlled Oscillator 1110. The result is that the signal is down converted to the base band with the carrier removed. There are other unwanted spectral components created by this process, namely a double time carrier side band, but these can easily be filtered out.

A combination decimator and digital filter 1120 follows the Digital Mixer 1118. This block performs sampling down conversion, reducing the sample rate from at least twice the carrier frequency to at least twice the pixel rate which is much lower. The digital filter would typically include a Cascaded Integrator Comb, or CIC filter, which removes the unwanted spectral byproducts of mixing as well as improving the receiver signal to noise. A CIC filter provides a highly efficient way to create a narrow passband filter after mixing the signal down to baseband with the digital mixer. The CIC filter may be followed by a FIR filter running at the slower decimated rate to correct passband droop.

With a reduction of sample rate in the order of 100:1 a relatively small Control Processor Buffer (1132) could be used to capture and entire fingerprint. For example a 200×200 array producing 40 k pixels could be stored in a 40 kb buffer. This is in contrast to a swipe sensor which must scan the partial image frames at a rate fast enough to keep up with the fastest allowable swipe speed, usually around 200 ms. At the same time, a slow swipe of two seconds must also be accommodated, requiring ten times the amount of memory as the fastest one. Various techniques have been developed to throw away redundant sample lines before storage, but even with that the real time storage requirements are much greater for swipe sensors. This is a critical factor in Match on Chip applications where memory capacity is limited. In addition, a placement sensor has no real-time data acquisition or processing requirements on the host processor beyond the patience of the user for holding their finger in place.

Referring to FIG. 12, and example of a sensor 1200 configured according to one embodiment of the invention is illustrated in a configuration that is known in the fingerprint industry as a Chip on Flex. Chip on Flex is a configuration where a processor chip is attached to a flexible substrate, such as Kapton™ tape, and that is electrically connected to conductive lines and possibly other components located on the flexible substrate. The example shown illustrates an integrated circuit 1210, which may be a logic circuit formed on a silicon substrate, a microprocessor, or other circuit for processing pixel information captured from a sensor circuit.

If configured as a fingerprint sensor or other placement sensor, integrated circuit 1210 may be a mixed signal chip that enables all or some of the functions described in FIG. 16 below. In one embodiment, it has enough inputs and outputs to drive a 200 by 200 line array of drive and pickup lines, and may have more or less of either lines. The top layer 1220 is formed by an array of pickup lines connected directly to integrated circuit 1210. This may be a flip chip mounted directly to the flex substrate without bond wires. In this example, the bottom layer is formed by folding the single layer back onto itself along the folding axis 1230 to create double layer active sensor area 1255. The drive lines fold to create the bottom layer 1225. The drive lines in this example are split into left and right groups 1240 and 1242 respectively for the sake of layout balance, but could be all on the left or right side of the sensing area. The left drive plate bundles 1240, and right drive plate bundles 1242 are inter-digitated with alternating left and right feeds to form a continuous line array on bottom layer 1225.

Flexible substrate based connector 1235 routes power, ground and interface signals out to an external host or onto another substrate that contains system level components, such as those illustrated in FIG. 16 and described below. These components may include but are not limited to a processor with memory, logic enabling imbedded matching algorithm(s) and encrypting/decrypting functions. In an alternative example, connector 1235 may be attached to the host substrate using conductive adhesive otherwise known as anisotropic conductive film (ACF attach), which may be labeled as “high density” in some products.

Referring to FIG. 13a , an illustration of a flex layout structure 1300 is illustrated. As shown, the flex layer structure 1300 includes an imaging area 1350, in which drive lines form crossover locations with pickup lines, where the crossover locations are formed by folding the top layer 1370 over bottom layer 1372, folding the flexible substrate upon itself about flex bend radius 1374. From a side view, the top flex 1364 is layered over top solder mask 1362, which is layered upon top copper or pickup lines 1360. Bottom layer solder mask 1370 is folded under top copper 1360, and bottom copper 1372 is formed under solder mask 1370 and over bottom flex 1375.

Referring to FIG. 13b , an example of a module structure 1301 is shown for mounting the flex layer structure 1300 of FIG. 13a . Those skilled in the art will understand that the structure of a particular module may vary according to the invention, and that this example, though it shows a substantially complete example of a module that can be used to base a practical implementation, is but one example and is not intended and should not be considered as limiting the invention in any way. The example structure 1301 includes rigid substrate 1330 that receives the flex top layer 1370 on its top layer with flex locating pins or plastic frame 1337 configured to ensure alignment of the drive plates with the pickup plates. Because the sensing electrode pairs are formed by crossovers of the drive and pickup lines on the two layers, the x-y alignment tolerance requirements may be on the order of several pixels, rather than the sub-pixel alignment tolerances that would be required if there were features to be matched between the two layers. The four mounting holes (1337) on each layer are sufficient to ensure angular and x-y alignment. Also illustrated is driver chip 1310 and imaging area 1350.

Referring to FIG. 14, an illustration is provided of an example system 1400 incorporating a sensor system 1402 generally configured according to the invention. A sensor device may be incorporated into a system, or may be configured as a stand-alone product. As a stand-alone product, the sensor components may be encased in a housing (not shown), and electrical connections exposed for connection to a device or system that would utilize such a device. Those skilled in the art will immediately see how a sensor configured according to the invention as described herein can be incorporated into a housings that are widely used in different industry sectors. Thus, for example, in a system, the mechanical connections, designs and structures may necessarily vary according to a particular application. For example, if incorporated into a laptop for use as a fingerprint sensor, a surface mounting module would need to be employed to expose the sensor grid lines to a user. If incorporated into a mobile phone, personal data assistant (PDA) or the like, another type of mounting module would be needed to conform to the particular device design while providing the operational capability of the sensor. Again, FIG. 14 illustrates a diagrammatic representation of a system 1400 that incorporates a sensor 1402 configured according to the invention with the folded flexible or rigid substrate 1404 having a top layer 1406 and a bottom layer 1408, and each having either pickup lines or plates and drive lines or plates respectively depending on the application, though not shown here. The two-dimensional sensing area 1411 is shown with an object 1410 on top, which may be a finger in the case of a fingerprint sensor, or another object in another application. The top layer's pickup plates or lines (not shown) communicate with top plate processing circuitry 1410 via communication link 1412 to send resultant signals received. Drive lines or plates are located but not shown here on bottom layer 1408, and receive drive signals from bottom plate processing circuitry 1414 via communication line 1416. The top plate processing circuitry 1410 includes front end buffers and amplifiers 1416 configured to receive, amplify and/or buffer or store a resultant signal received from the pickup plates or lines. A switch array 1418 such as that illustrated in FIG. 9 is configured to receive the signal from the front end 1416 and send the switched signal to analog to digital (A/D) converter 1420 for conversion to a digital signal. Digital signal processor (DSP) 1422 is configured to receive the digital signal from A/D converter 1420 and process the signal for transmission.

Bottom plate processing circuitry 1414 is configured to produce a drive signal for use by drive plates or lines located on the bottom layer 1408 of the sensor substrate 1404, and includes drivers and scanning logic 1424 for producing the signal, and programmable frequency generate 1426 for programmable setting the frequency in which the drive signal is set. The bottom plate processing circuitry 1414 includes communication link 1428, likewise, top plate circuitry has communication link 1420 for communicating with system buss 1432 for sending and receiving communications among the system, such as to processors, memory modules, and other components. System buss 1432 communicates with persistent memory 1434 via communication link 1436 for storing algorithms 1428, application software 1440, templates 1442, and other code for persistent and frequent use by processor 1444. Processor 1444 includes processor logic having logic and other circuitry for processing signals received from the system buss and originating from the sensor 1402, and also includes arithmetic logic unit 1450 configured with logical circuits for performing basic and complex arithmetic operations in conjunction with the processor. Processor memory 1452 is configured for local storage for the processor 1444, for example for storing results of calculations and retrieval for further calculations.

In operation, drive signals are controlled by processor 1444, and parameters for the drive signals originating from bottom plate processing circuitry 1414 are set in the bottom plate processing circuitry 1414 by the processor 1444. Drive signals are generated by logic 1424 within the parameters set in generator 1426 and sent to bottom plate 1408 via communication link 1416. These signals generate electromagnetic fields that extend to pickup lines on top layer 1406 about the sensing area 1411. These signals are cycled through different pixel electrode pairs on the sensor grid (not shown here, but described above), and some of these electromagnetic fields are absorbed by the object 1410 (such as a fingerprint for example). The resultant signal is picked up by the pickup plates or lines located on top layer 1406 about the sensing area (not shown here, but described above). The resultant signal is then transmitted to top plate processing circuitry 1410 via communication line 1412, and the signal is processed and transmitted to storage or processor 1444 for further processing. Once the drivers and scanning logic have cycled through the pixels on the grid sensor, data related to features and characteristics of the object can be defined and utilized by the system. For example, in a fingerprint sensor system, the image may be a fingerprint image that can be compared to a stored fingerprint image, and, if there is a match, it can be used to validate a user.

FIG. 15 Illustrates how a device configured according to the invention may be applied to a fingerprint sensing application. A user places a finger with fingerprint (1510) over the sensor grid, which is formed by the crossover locations of the drive plates (1506 a-1506 n) and the pickup plates (1502 a-1502 m). Image pixel 1561 a senses the fingerprint area above the electrode pair of drive plate 1506 a and pickup plate 1502 a, pixel 1561 a senses the crossover of drive 1506 n and pickup 1502 a, and pixel 1562 n senses the area above the crossover of drive 1506 n and pickup 1502 m

FIG. 16 illustrates the steps required to collect the fingerprint image as shown in FIG. 15, using the embodiment of the invention shown in FIGS. 11 and 14. Image capture begins at step 1601. As part of the initialization a row counter is initialized to 1 at step 1602. Step 1603 is the beginning of a row scan sequence. At the beginning of each row, a column counter is set to 1 at step 1603. In step 1604, the top plate scanning logic 1145 activates the appropriate analog switch (one of 1103 a through 1103 n) for the selected row. In Step 1605 the sense of an individual pixel begins when the bottom plate scanning logic 1140 activates the appropriate drive plate (one of 1106 a through 1106 n) with the carrier signal 1116. At step 1606 the signal from differential amplifier 1180 is sampled repeatedly by A/D converter 1125 after processing through programmable gain amplifier 1190. Digital mixer 1118 mixes the samples down to the baseband frequency set by digital oscillator 1110. The baseband signal is then filtered by digital decimating filter 1120 to produce a signal level value for the current pixel. The functions performed for this step in the embodiment of FIG. 11 could alternatively be performed by the corresponding analog receiver shown in FIG. 10, or other functionally similar arrangements. In step 1607 the signal level value derived in step 1606 is stored in the appropriate position in memory buffer 1132 which corresponds to the currently selected row and column. In step 1608 the column number is incremented, and in step 1609 the column number is tested to determine whether the current row collection has been completed. If the row has not been completed, we return to step 1605 to collect the next pixel in the row. If the row is complete, we proceed to step 1610 and increment the row number. In step 1611, we test the row number to determine if all the rows have been scanned. If not, flow returns to 1603 to start the next row back at the first column. Once all the rows have been scanned, image capture is complete, and we proceed to step 1612, at which point the image is ready for further processing or transfer to long term storage.

Those skilled in the art will recognize that row and column scanning order may not correspond directly to physical position in the array, as some implementations may more optimally be sampled in interleaved fashions.

In FIG. 17, an example of the example as shown in FIG. 14 in a user authentication application. In step 1701 a system level application 1440 on processor 1444 requires user authentication. At step 1702 the user is prompted to provide a finger for verification. The system waits for finger presence to be detected in step 1703. This can be performed by collecting a reduced size image as described in FIG. 16 and testing for finger image, or via other dedicated hardware. Once finger presence is detected, a complete image is collected in step 1704, using the method described in FIG. 16 or other substantially similar method. This image is then stored and in step 1705 converted into a template 1712 as shown in FIG. 17B, typically consisting of a map of minutia point locations and types (such as bifurcations 1710, and terminations 1711), or possibly of ridge frequency and orientation, or some combination of both. In step 1707 the template is then compared against one or more enrollment templates that were retrieved from persistent template storage 1142 in step 1706. If a match is found, the user is authenticated in step 1708 and granted access to the application. If no match is found, the user is rejected in step 1709, and access is denied.

While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention is not limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. Hence, alternative arrangements and/or quantities of, connections of various sorts, arrangements and quantities of transistors to form circuits, and other features and functions can occur without departing from the spirit and scope of the invention. Similarly, components not explicitly mentioned in this specification can be included in various embodiments of this invention without departing from the spirit and scope of the invention. Also, different process steps and integrated circuit manufacture operations described as being performed to make certain components in various embodiments of this invention can, as would be apparent to one skilled in the art, be readily performed in whole or in part to make different components or in different configurations of components not explicitly mentioned in this specification without departing from the spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention is not limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

Again, the invention has application in many areas, particularly in biometric sensors. Fingerprint sensors, for example, and other biometric sensors are gaining increasing acceptance for use in a wide variety of applications for security and convenience reasons. Devices, systems and methods configured according to the invention will have improved security of the biometric verification process without increasing the cost of the system. Furthermore, the invention may extend to devices, systems and methods that would benefit from validation of components. As discussed above, the invention includes the ability for the host and sensor to include any combination or subset of the above components, which may be arranged and configured in the manner most appropriate for the system's intended application. Those skilled in the art will understand that different combinations and permutations of the components described herein are possible within the spirit and scope of the invention, which is defined by the appended Claims, their equivalents, and also Claims presented in related applications in the future and their equivalents.

The invention may also involve a number of functions to be performed by a computer processor, such as a microprocessor. The microprocessor may be a specialized or dedicated microprocessor that is configured to perform particular tasks according to the invention, by executing machine-readable software code that defines the particular tasks embodied by the invention. The microprocessor may also be configured to operate and communicate with other devices such as direct memory access modules, memory storage devices, Internet related hardware, and other devices that relate to the transmission of data in accordance with the invention. The software code may be configured using software formats such as Java, C++, XML (Extensible Mark-up Language) and other languages that may be used to define functions that relate to operations of devices required to carry out the functional operations related to the invention. The code may be written in different forms and styles, many of which are known to those skilled in the art. Different code formats, code configurations, styles and forms of software programs and other means of configuring code to define the operations of a microprocessor in accordance with the invention will not depart from the spirit and scope of the invention.

Within the different types of devices, such as laptop or desktop computers, hand held devices with processors or processing logic, and also possibly computer servers or other devices that utilize the invention, there exist different types of memory devices for storing and retrieving information while performing functions according to the invention. Cache memory devices are often included in such computers for use by the central processing unit as a convenient storage location for information that is frequently stored and retrieved. Similarly, a persistent memory is also frequently used with such computers for maintaining information that is frequently retrieved by the central processing unit, but that is not often altered within the persistent memory, unlike the cache memory. Main memory is also usually included for storing and retrieving larger amounts of information such as data and software applications configured to perform functions according to the invention when executed by the central processing unit. These memory devices may be configured as random access memory (RAM), static random access memory (SRAM), dynamic random access memory (DRAM), flash memory, and other memory storage devices that may be accessed by a central processing unit to store and retrieve information. During data storage and retrieval operations, these memory devices are transformed to have different states, such as different electrical charges, different magnetic polarity, and the like. Thus, systems and methods configured according to the invention as described herein enable the physical transformation of these memory devices. Accordingly, the invention as described herein is directed to novel and useful systems and methods that, in one or more embodiments, are able to transform the memory device into a different state. The invention is not limited to any particular type of memory device, or any commonly used protocol for storing and retrieving information to and from these memory devices, respectively.

The term “machine-readable medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of instructions. The term “machine-readable medium” shall also be taken to include any medium that is capable of storing, encoding or carrying a set of instructions for execution by the machine and that causes the machine to perform any one or more of the methodologies of the present invention. The machine-readable medium includes any mechanism that provides (i.e., stores and/or transmits) information in a form readable by a machine (e.g., a computer, PDA, cellular telephone, etc.). For example, a machine-readable medium includes memory (such as described above); magnetic disk storage media; optical storage media; flash memory devices; biological electrical, mechanical systems; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). The device or machine-readable medium may include a micro-electromechanical system (MEMS), nanotechnology devices, organic, holographic, solid-state memory device and/or a rotating magnetic or optical disk. The device or machine-readable medium may be distributed when partitions of instructions have been separated into different machines, such as across an interconnection of computers or as different virtual machines.

While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

Reference in the specification to “an embodiment,” “one embodiment,” “some embodiments,” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments. The various appearances “an embodiment,” “one embodiment,” or “some embodiments” are not necessarily all referring to the same embodiments. If the specification states a component, feature, structure, or characteristic “may”, “might”, or “could” be included, that particular component, feature, structure, or characteristic is not required to be included. If the specification or Claim refers to “a” or “an” element, that does not mean there is only one of the element. If the specification or Claims refer to “an additional” element, that does not preclude there being more than one of the additional element.

The methods, systems and devices include improved security operations and configurations with a novel approach to biometric systems. Such systems would greatly benefit from increased security features, particularly in financial transactions. Although this embodiment is described and illustrated in the context of devices, systems and related methods of validating biometric devices such as fingerprint sensors, the scope of the invention extends to other applications where such functions are useful. Furthermore, while the foregoing description has been with reference to particular embodiments of the invention, it will be appreciated that these are only illustrative of the invention and that changes may be made to those embodiments without departing from the principles of the invention, the scope of which is defined by the appended Claims and their equivalents. 

The invention claimed is:
 1. An fingerprint impedance sensor, comprising: a plurality of substantially parallel drive lines; a plurality of substantially parallel pickup lines oriented substantially perpendicular to the drive lines and physically separated from the drive lines by a substantially incompressible dielectric located between the drive lines and pickup lines to form a plurality of impedance sensitive crossover locations where a pickup line crosses a drive line; and circuitry that includes a signal generator connected to the drive lines, and configured to: sequentially activate each of the drive lines by transmitting a signal to each of the drive lines, one at a time, and grounding the remaining drive lines while the signal is being transmitted to the one activated drive line to thereby cause an electric field to radiate from the one activated drive line toward the pickup line at each of the impedance sensitive crossover locations formed by the activated drive line, for each drive line that is activated, sequentially measure an amount of the electric field on each of the pickup lines at each of the impedance sensitive crossover locations and ground the remaining pickup lines while the electric field is being measured at the one pickup line, and distinguish between different surface features of a proximally located finger at each of one or more of the impedance sensitive crossover locations based on the amount of the electric field measured at the crossover location.
 2. The fingerprint impedance sensor according to claim 1, wherein the dielectric includes at least one of a rigid substrate, glass, ceramic, and a rigid board.
 3. The fingerprint impedance sensor according to claim 1, wherein the circuitry is configured to distinguish between a fingerprint valley and a fingerprint ridge at one or more of the crossover locations based on the amount of the electric field measured at the crossover location.
 4. The fingerprint impedance sensor according to claim 1, wherein the circuitry further comprises scanning logic configured to sequentially scan a plurality of crossover locations formed by the plurality of pickup lines.
 5. The fingerprint impedance sensor according to claim 4, wherein each of the crossover locations corresponds to a pixel of image information, and the scanning logic is configured to capture a plurality of pixels corresponding to a plurality of crossover locations.
 6. The fingerprint impedance sensor according to claim 1, wherein the signal generator is configured to generate a signal having multiple frequencies.
 7. The fingerprint impedance sensor according to claim 1, wherein the crossover locations form a finger contact area, the sensor further comprising: a reference line located outside the finger contact area; and a differential amplifier configured to subtract a signal on at least one of the plurality of pickup lines against a signal on the reference line.
 8. The fingerprint impedance sensor according to claim 7, wherein the distance between the reference line and a closest one of the plurality of pickup lines is greater than the distance between adjacent lines of the plurality of pickup lines.
 9. The fingerprint impedance sensor according to claim 7, wherein the reference line is positioned under a component that prevents finger contact with the reference line.
 10. The fingerprint impedance sensor according to claim 9, wherein the component comprises plastic material of a bezel.
 11. The fingerprint impedance sensor according to claim 1, wherein the dielectric is a folded rigid substrate having a top layer and a bottom layer, wherein each of the top layer and the bottom layer has the plurality of drive lines or the plurality of pickup lines located on the layer.
 12. The fingerprint impedance sensor according to claim 1, wherein the dielectric is a folded substrate that has the plurality of drive lines and the plurality of pickup lines located on the substrate, and wherein the plurality of drive lines is divided into a first bundle of drive lines and a second bundle of drive lines that are separated by at least one of the plurality of pickup lines.
 13. The fingerprint impedance sensor according to claim 1, wherein the dielectric has a dielectric constant that is greater than
 1. 14. The fingerprint impedance sensor according to claim 1, wherein the circuitry is configured to both detect a fingerprint of a proximally located finger and to track motion of the finger. 